It is noticed that chlorine, sulfur, alkali and the like cause troubles such as preheater clogging in cement plants, and especially chlorine exerts the most harmful effect, so that a cement kiln chlorine/sulfur bypass system that bleeds a kiln exhaust gas passage, which runs from the end of a cement kiln to a bottom cyclone, of a part of the combustion gas to remove chlorine is used.
In this cement kiln chlorine/sulfur bypass system, as exemplarily described in World Patent Publication WO97/21 pamphlet, chlorine is more distributed on fine particle side of the dust, which is generated by cooling the bled exhaust gas, so that the dust is separated into coarse particles and fine particles by a classifier; the coarse particles are returned to the cement kiln system; and the fine particles (chlorine bypass dust) containing separated potassium chloride (KCl) and the like is recovered to be added to a cement grinding mill system.
However, in recent years, recycling of waste through conversion to cement raw material or fuel is promoted, which increases the quantity of volatile components, such as chlorine, sulfur, alkali and the like, brought to the cement kiln, as the quantity of the treated waste increases, which increases the quantity of the chlorine bypass dust generated. As a result, all of the chlorine bypass dust cannot be utilized in the cement grinding process, and salt that is not utilized is discharged after water treatment. However, it is expected that the quantity of the chlorine bypass dust will further increase in future, development of a new processing method is desired.
From the above-mentioned point of view, as described in Japanese Patent Publication Heisei 11-100243 gazette, in order to desalt chlorine bypass dust and the like conventionally subjected to water treatment and effectively utilize the desalted matter as cement raw material, water is added to a waste containing chlorine to elute chlorine; and the resulting material is filtered; and desalted cake is utilized as cement raw material; and drainage is purified and is discharged without causing environmental pollution to treat the chlorine bypass dust.
However, in the conversion treatment of waste into cement raw material described in the above Japanese Patent Publication Heisei 11-100243 gazette, in order to desalt chlorine bypass dust and the like, a cooler (heat exchanger) and a hot bag filter are used to recover the chlorine bypass dust, but the chlorine bypass dust contains salt, so that the cooler and the like are easily corroded, which shortens the life of the equipment, in addition, a large-scale tank and fixed-quantity feeders are required to storage a large amount of dust, of which specific gravity is considerably low and which is difficult to handle, which causes a problem that equipment cost increases.
Further, at the above chlorine bypass, a part of combustion gas bled from the cement kiln at a portion near the inlet hood thereof contains sulfur, so that the bled gas cannot be discharged to outside as it is, and the gas is required to be returned to a raw material drying process, raw material grinding process, or the like.